Senior US officials were engaged last night in last-ditch efforts to persuade Turkey not to launch a major military incursion into Iraqi Kurdistan to target armed separatists.

A team was diverted from a mission to Russia to make an unscheduled stop in Ankara yesterday. Against the background of the escalating diplomatic row between Turkey and the US over a congressional resolution that branded as 'genocide' massacres of Armenians by Ottoman Turks in 1915, US Secretary of State, Condoleezza Rice, revealed she had personally urged Turkey to refrain from any major military operation in northern Iraq. The row between the two Nato allies comes against the dangerous background of a threat by the Turkish parliament to approve this week a 'hot pursuit' of the Kurdish separatist Kurdistan Workers' Party, the PKK, across the border into northern Iraq.

The threat of military action came after last Sunday's killing by the PKK of 13 Turkish soldiers in an ambush in Sirnak province, close to the Iraqi border.

'I urged restraint,' said Rice, on a visit to Moscow, acknowledging 'a difficult time' between the two countries as she described her telephone conversations with Turkey's President Abdullah Gul, its Prime Minister and foreign minister.

'It's a difficult time for the relationship,' Rice said. 'We just thought it was a very good idea for two senior officials to go and talk to the Turks and have reassurance to the Turks that we really value this relationship.' Rice said that in her conversation with the Turks 'they were dismayed' by the congressional resolution. 'The Turkish government, I think, is trying to react responsibly. They recognise how hard we worked to prevent that vote from taking place.'

About 60,000 Turkish troops are based near the northern Iraqi border. US military officials have said they believe they will get some warning if the Turks attack the PKK.

Rice's phone conversations came as two senior US officials flew to Turkey yesterday to attempt to defuse tension that has seen the Turkish ambassador to Washington return home for consultations following the resolution, which Turks regard as deeply offensive.

US Assistant Secretary of State Dan Fried and US Under Secretary of Defence Eric Edelman flew from Moscow, where they had been accompanying Rice. It was reported that Edelman said on his arrival they were visiting Turkey to express regret over the approval of the resolution. The pair are likely to hear sharp criticism from the Turkish government.

'They are sure to raise the northern Iraq issue, but from our perspective the top issue is the Armenian resolution,' a Turkish diplomat said. The row between the two allies follows the decision by the Foreign Affairs Committee of the House of Representatives to approve a resolution labelling the 1915 killings genocide, rejecting appeals by President Bush. Turkey denies genocide but says many died in inter-ethnic fighting in an issue that is still deeply sensitive to Turks.

Turkish officials say foreign ministry and military officials met after the resolution was approved to discuss potential measures against the US. In initial repercussions, a US visit by Trade Minister Kursad Tuzmen was cancelled, along with a conference being held by the Turkish-US Business Council.

Other potential moves may include blocking US access to Incirlik air base, cancelling procurement contracts, scaling down bilateral visits, denying airspace to US aircraft and halting joint military exercises, say analysts and diplomats.

The US relies heavily on Turkish bases to supply its war effort in Iraq. Ankara has long complained Washington has not done enough to crack down on PKK rebels who use northern Iraq as a base to attack Turkey. The PKK said on Friday its guerrillas were crossing back into Turkey to target politicians and police after the prospect of a cross-border military operation emerged. Turkey blames the PKK for the deaths of more than 30,000 people since the group launched its armed struggle for an ethnic homeland in south-east Turkey in 1984.